The present invention relates to an improved drive system wherein a first component applies a driving torque to a second component, such as for example a threaded fastener and driver combination.
Designers and engineers have experimented with various configurations for torque transmitting drive systems. These drive systems may be employed in various types of applications wherein it is desired to transmit torque from one component to another. A particular application for which the present invention was primarily developed and with regard to which the following description relates, is the driving of threaded fasteners, such as screws and bolts.
The prior art is replete with various forms or designs of drive systems where one component is recessed while the other is provided with a complementary shaped projection for disposition in the recess. In this regard, either the recessed member or the projecting member may be the drive tool, and correspondingly the driven member may be provided with either a recess or a complementary shaped projection. By way of example, attention is invited to U.S. Pat. No. 2,397,216 to Stellin, dated Mar. 26, 1946 which discloses numerous forms or shapes of drive systems. Attention is also directed to U.S. Pat. No. 3,584,667 which illustrates a drive system which has gained wide acceptance in the automotive, aerospace and appliance industries and which is marketed under the brand name TORX.RTM.. In addition, of course, there are other well-known hex-type drive systems, as well as cruciform-type drive systems such as the PHILLIPS.RTM. drive system. Finally, there are systems which utilize various splined configurations somewhat along the lines of the above-referenced TORX.RTM. drive system. Representative samples of the splined-type system can be found in U.S. Pat. No. 3,888,480 to Herman G. Muenchinger dated May 27, 1975; U.S. Pat. No. 2,803,092 to J. R. Richer, dated Jun. 8, 1937; U.S. Pat. No. 2,969,250, dated Jan. 24, 1961 to F. R. Kull and U.S. Pat. No, 4,006,660 dated Feb. 8, 1977 to Yamamoto et al.
The various drive systems of the prior art have been designed with a view toward handling of the forces created during driving of the fastener. In this regard, a vector analysis of the forces generated indicates that a component of the applied force will be directed radially outwardly, while a second component will be directed tangentially. It is only the tangential component of the applied force which serves to rotate or drive the fastener, viz., is converted to driving torque. As a term of art, designers often reference the system "drive angle", which is defined by the angle made by a line tangent to the point of driver contact at the point of application and a radial line through the fastener or drive tool per se. Generally speaking, the lower the "drive angle", the more efficient the drive system in that the "drive angle" determines the amount of applied force that is directed tangentially and thus is converted to driving torque. Further, it has also been found that with the drive angle that exceeds a certain value, as for example 60.degree., the torque loss is excessive. That is, most of the applied force will be directed radially, with only a small tangential component. This situation is to be avoided, as an excessively large radial component can severely damage the socketed component of the drive system.
The prior art systems using a multiplicity of splines which are of a relatively square configuration, will attain a low drive angle, zero or less, i.e. a negative angle or at zero. These designs, however, have not proven practical in service, nor in production. These types of drive systems are difficult and expensive to produce and often require special machining operations. Most importantly, the square corners result in stress risers which can lead to fatigue failure over extended periods of use. As to the spline-type drive systems which utilize a plurality of oppositely curved surfaces which are uniformly deployed about the 360.degree. circumference of the components to form an alternating series of lobes and flutes, these drive systems overcome some of the problems inherent in square spline systems mentioned above, but are not generally capable of attaining a low drive angle, i.e. less than five degrees. That is to say, upon the application of extremely high torque, a radial force component will be created which can lead to socket failure or a tendency to shear or wipe out the lobe configurations.
To a great extent, the problems with the prior art splined type designs were overcome with the TORX.RTM. drive system as disclosed in U.S. Pat. No. 3,584,667. This drive system employs a hexlobular configuration based upon mating arcuate surfaces designed to attain drive angles within the range of 10.degree.-20.degree.. While the TORX.RTM. brand drive system was an advance in the art and has proven extremely beneficial and satisfactory in service, there are certain aspects of this system that could be improved. In one respect, as the manufacturing tolerances vary due to tool wear or to other variances in the dimensions of the forming tools for the fastener and driver surfaces, the point of contact between the fastener and driver will move inwardly or outwardly along the curved surfaces, thus altering the drive angle.
In addition, as the point of contact moves radially outward, bit or drive tool strength is sacrificed. More specifically, the strength of the drive tool lobes is directly related to the axial cross-section through the lobe at the point of contact. It can be appreciated that with this prior art type drive tool, shown in FIG. 8, as the point of contact moves outwardly, the axial cross-sectional area through the lobe at the point of contact will decrease, resulting in a decrease in bit strength, viz. the tools ability to transmit high torque values without the lobes shearing or failing. As will become clear from the discussion to follow, with the design of the present invention, the point of contact remains relatively constant. Thus, variances or tolerances encountered in manufacturing of the drive system components will not materially alter or adversely affect the strength of the bit.
Also, with extremely small sizes, there is a tendency for the lobes on either the fastener or driver to deform under operating conditions. In addition, where the fastener is provided with an internal recess or socket and the driver is the male member of the drive system, it is not always possible to obtain sufficient driver strength for long-term operation.